onDraw method of the PianoView for the SSaurel's Channel

PianoView.java

@Override
protected void onDraw(Canvas canvas) {
  for (Key k : whites) {
    canvas.drawRect(k.rect, k.down ? yellow : white);
  }

  for (int i = 1; i < NB; i++) {
    canvas.drawLine(i * keyWidth, 0, i * keyWidth, height, black);
  }

  for (Key k : blacks) {
    canvas.drawRect(k.rect, k.down ? yellow : black);
  }
}